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TOC Alert for Publication# 58 2018February 15652C1C41167652C2C2679652135136414${d}$ ) of 100, 200, 400, and $600~mu text{m}$ . Theoretical and experimental sensitivities agreed to within 12 ± 3% [root-mean-square (RMS) normalized magnitude ratio] and 8° ± 3° (RMS phase difference) for the four hydrophones over the range from 1 to 10 MHz. The model predicts that distortions in peak positive pressure can exceed 20% when $d/lambda _{0} < 0.5$ and spectral index (SI) >7% and can exceed 40% when $d/lambda _{0} < 0.5$ and SI >14%, where $lambda _{0}$ is the wavelength of the fundamental component and SI is the fraction of power spectral density contained in harmonics. The model predicts that distortions in peak negative pressure can exceed 15% when $d/lambda _{0} < 1$ . Measurements of pulse distortion using a 2.25 MHz source and needle hydrophones with $d =200$ , 400, and $600~mu text{m}$ agreed with the model to within a few percent on the average for SI values up to 14%. This paper 1) identifies conditions for which needle and fiber-optic hydrophones produce substantial distortions in acoustic pressure pulse measurements and 2) offers a practical deconvolution method to suppress these distortions.]]>6521371481720in vivo human super-resolution imaging with ultrafast plane-wave imaging. The rich spatiotemporal information provided by ultrafast imaging presents features that allow microbubble signals to be separated from background noise. In addition, the high-frame-rate recording of microbubble data enables the implementation of robust tracking algorithms commonly used in particle tracking velocimetry. In this paper, we applied the nonlocal means (NLM) denoising filter on the spatiotemporal domain of the microbubble data to preserve the microbubble tracks caused by microbubble movement and suppress random background noise. We then implemented a bipartite graph-based pairing method with the use of persistence control to further improve the microbubble signal quality and microbubble tracking fidelity. In an in vivo rabbit kidney perfusion study, the NLM filter showed effective noise rejection and substantially improved microbubble localization. The bipartite graph pairing and persistence control demonstrated further noise reduction, improved microvessel delineation, and a more consistent microvessel blood flow speed measurement. With the proposed methods and freehand scanning on a free-breathing rabbit, a single microvessel cross-sectional profile with full-width at half-maximum of $57~mu text{m}$ could be imaged at approximately 2-cm depth (ultrasound transmit center frequency = 8 MHz, theoretical spatial resolution $sim 200~mu text{m}$ ). Cortical microvessels that are $7-
~mu text{m}$ apart can also be clearly separated. These results suggest that the proposed methods have good potential in facilitating robust in vivo clinical super-resolution microvessel imaging.]]>652149167729265216817713726521781872106Ex Vivo Kidneys]]>$A$ can be estimated. To evaluate the feasibility of estimating $A$ , we evaluated ten ex vivo porcine kidneys embedded in 10% porcine gelatin to mimic the case of a transplanted kidney. Under assumptions of an elastic incompressible medium for AE measurements, the shear modulus was quantified at each compression level and the applied strain was assessed by measuring the change in the thickness of the kidney cortex. Finally, $A$ was calculated by applying the AE theory. Our results demonstrated that it is possible to estimate a nonlinear shear modulus by monitoring the changes in strain and ${mu }$ due to kidney deformation. The magnitudes of $A$ are higher when the compression is performed progressively and when using a plate attached to the transducer. Nevertheless, the values obtained for $A$ are similar to those previously reported in the literature for breast tissue.]]>6521882002217in vivo. A continuous real-time refresh rate of 36 Hz was achieved in duplex combination with a standard B-mode at pulse repetition frequency of 8 kHz. Accuracies of −11% on velocity and of 2°on angle measurements have been obtained in phantom experiments. Accompanying movies show how the method improves the quantitative measurements of blood velocities and details the flow configurations in the carotid artery of a volunteer.]]>6522012091806$in~vivo$ volunteer data sets, the mean contrast ratio between the vertebrae surface and the surrounding tissue for DAS, Wiener, PCF, CF, GCF, and the proposed AAF methods are 0.49, 0.64, 0.82, 0.77, 0.76, and 0.91, respectively. The contrast is significantly improved in the proposed method.]]>65221022220991/3Nb2/3)O3-PbTiO3 (PMN-PT) polycrystalline ceramic with ultrahigh relative clamped dielectric permittivity ($varepsilon ^{S}/varepsilon _{0} = 3500$ ) and high piezoelectric properties ($d_{33}= 1200$ pC/N, $k_{t} = 0.55$ ) was used to fabricate high-frequency miniature ultrasound transducers. A 39-MHz high-frequency ultrasound needle transducer with a miniature aperture of 0.4 mm $times0.4$ mm was designed and successfully characterized. The fabricated needle transducer had an electromechanical coupling factor $k_{t}$ of 0.55, large bandwidth of 80% at −6 dB, and low insertion loss of −13 dB. A wire phantom and porcine eyeball imaging study showed good imaging capability of this needle transducer. The transducer performance was found to be superior to that of other needle transducers with miniature apertures, making this modified PMN-PT ceramic-based needle transducer quite promising for minimally invasive procedures in medical applications.]]>65222323022726522312433238652244257320465225826812986522692802176$lambda $ /4) low-loss alumina plates (${mathcal{ E}}_{r}= 9.75$ , loss tangent of $approx 1 times 10^{-5}$ to $2 times 10^{-5}$ ) mounted in a cylindrical metal waveguide. Tuning is achieved by varying the length of the center section of the cavity. A multi-element bellows/probe assembly is presented. A tuning range of 130 MHz (1.39%) is demonstrated. The insertion loss $S_{21}$ varies from −2.84 to −12.03 dB while the unloaded Q varies from 43 788 to 122 550 over this tuning range. At 10 of the 13 measurement points, the unloaded Q exceeds 1 00 000, and the insertion loss is above −7 dB. Two modeling techniques are discussed; these include a simple ABCD circuit model for rapid simulation and optimization and a 2.5-D field solver, which is used to plot the field distribution inside the cavity.]]>6522812913626652292294693